PURPOSE:To increase the discharge current by using a solid electrolyte composed of specific lithium-betaalumina containing silver or tellurium to improve the conductivity. CONSTITUTION:A solid electrolyte composed of (Li, Ag)-betaalumina or (Li, Tl)- betaalumina is used between a lithium positive and negative elecrodes to constitute a solid battery. The solid electrolyte is formed in such a way that Na-betaalumina is synthesised by hot press method, sliced to 0.3-1mm. thickness, and ionexchanged to obtain (Li, Ag)-betaalumina or (Li, Tl)-betaalumina. A positive electrode is formed by binary simultaneous evaporation, of a PbI2 and Pb and a negative electrode is by evaporation of Li metal, and (Li, Ag)-betaalumina obtained by above mentioned method is used as an electrolyte. Thus a solid battery with an opencircuit voltage of 2.04V and short-circuit current of 100-2,000muA can be obtained, and the discharge current can be increased by using the electrolyte with high conductivity.